What factors affect the gamut attainable on a particular paper?

Besides the characteristics of the paper itself, the main factor is:

• What Media Type was selected when the profile was made - there are a number of reports that the gamut can vary significantly depending on the Media Type selected. It is crucial to select the optimal media type, yet limited information is available (for non-Canon papers) on how to best do this. Known information is summarized on the Wiki page Creating Custom Profiles for Non-Canon Papers. For Canon papers, use the Media Type specified in Supported Canon Media